Transient electronics enabling devices to safely disappear in the environment can be applied not only in green electronics, but also in bioelectronic medicine. Neural implants able to degrade harmlessly inside the body eliminate the need for removal surgery, allow for safe tissue remodelling, and potentially reduce inflammation responses and the chronic adverse reactions hindering device functionality and putting patients' health at risk. Sadly, current transient neurotechnology can be used only for very short-term applications. Fast degrading metals generally used to build these interfaces allow in fact for operations rarely longer than a few days, strongly limiting the available time window for collecting information or for a therapy to be finished. To solve this problem, we propose a transient, all-polymeric neural interface able to work for longer time scales. This would enable new applications of transient neurotechnology, such as recording of brain activity for a prolonged and more useful period of time before resection of epilepsy foci or tumours. The device consists of a polycaprolactone (PCL) scaffold with patterned poly 3,4-ethylene dioxythiophene : polystyrene sulfonate (PEDOT:PSS) traces and electrodes. In vivo neural recording demonstrated low noise levels for twelve weeks and histological analysis highlighted the cellular infiltration inside the PCL scaffold over time, hinting to potential tissue remodelling processes, which would not occur with a non-degradable device. To increase the device potential for a clinical translation, a minimally invasive procedure for its implantation has been proposed. The blood vasculature supplying the brain and nerves can be used as an access route to the neural tissue, offering a close enough location without direct damage to the tissue. By re-shaping the all-polymeric transient neural probe using a stent-inspired design, the new interface can be navigated through a 5Fr catheter and deployed inside 2 mm-diameter channels. Characterization showed promising electrodes endurance to pulsatile flow and prolonged stimulation, together with a good safety profile. This device can be used for neural recording or stimulation from within a blood vessel, for either central or peripheral nervous system. By simplifying the implantation procedure of the neural interface and maintaining its transiency, physicians and patients could feel more confident in applying innovative neurotechnology-based treatments, widening for example the access to deep brain stimulation therapy. To enable crossing of complex vasculature without wall ruptures caused by current manual push of guidewires, a new navigation paradigm for endovascular devices has been designed and tested on thin polyimide strips. A physiological pulsatile flow can propel these probes, even at curvatures as high as 0.25 mm-1, and low amplitude magnetic fields can steer their direction. Electrodes and sensors for temperature and flow can be embedded onto these micro-probes, for unprecedented local interrogation of deep vasculature regions. In conclusion, this thesis introduces new neural interfaces in the field of minimally invasive neurotechnology, reducing adverse effects and complications of non-degradable implants and open surgery. These devices and their concepts have the potential one day to be new tools of the bioelectronic medicine toolbox, contributing to the advancement of innovative treatments for neurodegenerative disorders.